Revisiting player contributions in regularized adjusted plus-minus models: an application on NBA historical data

Abstract In basketball and other team sports, assessing players’ and lineups’ performances is crucial for team management. This assessment should address both individual players’ contributions and the synergies among them. Here, we aim to analyze the importance of collaboration among NBA players from the 2002–2003 to the 2022–2023 season. To this end, we propose a modification of the extended Regularized Adjusted Plus-Minus model, where the efficacy of each lineup is determined by adding up the non-negative contributions of players on the court, adjusted for a positive or negative interaction term. The proposed specification improves the readability of the estimated values of players’ and lineups’ effects, which can be straightforwardly visualized and used more efficiently for actual decision-making. The main analyses based on this model specification revealed that, in the NBA, the importance of synergies among players decreases over the years, suggesting a shift from team to individual-oriented style of play. The only notable exception occurs during the COVID-19 lockdown period, when the relevance of lineups effects temporarily increases, indicating a change towards a team-oriented style of play. The proposed model can also be adopted to evaluate the difference between home and away-specific performances of players and lineups.